Process for making tungsten carbide castings



Jan. 28, 1936.

O. F. MARVIN Filed March 19, 1932 PROCESS FOR MAKING TUNGSTEN CARBIDE CASTINGS 2 Sheets-Sheet l Jan. 28, 1936. o. F. MARVIN V PROCESS FOR MAKING TUNGSTEN CARBIDE CASTINGS Filed March 19, 1932 2 Sheets-Sheet 2 Car Patented Jan. 28, 1936 PATENT OFFICE PROCESS FOR MAKING TUNG STEN CARBIDE CASTINGS Orrin F. Marvin, Los Angeles, Calif., assig'nor to Mills Alloys, Inc., Los Angeles, Calif., a corporation of Delaware Application March 19, 1932, Serial No. 599,938

4 Claims.

This invention relates to a production of sharply defined cast bodies from diiiicultly fusible metals, such for example, as tungsten carbide and the like, and more particularly to an improvement over the co-pending application to Oscar L. Mills for a Tungsten carbide product and process of making same, Serial No. 455,732, filed January 17, 1931.

In the above mentioned co-pending application a process is described for producing a cast article of manufacture from molten tungsten carbide which is characterized by a fine grained structure. In this process, a molten tungsten carbide mass is first produced at a temperature above its melting point; as for example, by the aid of the inventions disclosed in the prior patents to Oscar L. Mills, No. 1,718,558, issued July 2, 1929 and No. 1,721,966, issued July 23, 1929. This mass preferably has, by weight, not less than 2 percent of carbon, nor more than 6 percent thereof.

When this material is thoroughly and completely molten, as in a carbon crucible capable of accommodating at least several pounds thereof, it is poured into a mold of the desired configuration, and subjected to pressure for the purpose of securing a fine grain structure. This is accomplished by the aid of centrifugal force; which is produced by providing a rotating mold structure, which in rotating throws the molten material against the walls thereof.

I have found that a uniform and fine grained product can be obtained by the use of a double or combination mold structure, comprising essentially an inner graphite mold proper and an outer mold or support of copper or silver, with the application of pressure, as for example by centrifugal force. This double mold allows the cast ing to chill slowly enough in order to reduce the possibility of producing internal strains. The graphite shell comprising the mold proper is made so that it retains the heat for a sufficient period to effect this result; and this heat retention property must be enhanced by the aid of further heat insulation, as by an air space, between the copper and the graphite mold. Furthermore, the insulation acts to keep the graphite mold from transferring or absorbing any material amount of heat from the cast alloy, thereby retaining this heat for a long period and preventing unequal or deleterious or partial cooling.

It is a further object of my invention to provide a process for producing sharply defined tungsten carbide articles in commercial quant ties, with a minimum expense and expenditure of time, and particularly by casting the article to be formed directly in complete form.

Although I prefer to utilize tungsten carbide without the addition of any other element, a small percentage of free carbon or of other ma- 6 terial such as boron, silicon, cobalt, nickel or chromium may be employed, but only to a sparing extent, because such admixtures tend to destroy the copper parts of the mold. Such alloying materials, which of course tend materially to 10 reduce the hardness of the product, are not essential in my process, because I secure the desired structure due to my improved treatment of the molten material.

My invention possesses many other advantages, and has other objects which may be made more easily apparent from a consideration of several embodiments of my invention. For this purpose I have shown a few forms in the drawings accompanying and forming part of the present speciflcation. I shall now proceed to describe these forms in detail, which illustrate the general principles of my invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of my invention is best defined by the appended claims.

Referring to the drawings:

Figure 1 is a diagrammatic side elevation of an apparatus utilized in my invention;

Fig. 2 is a fragmentary plan view thereof;

Fig. 3 is a fragmentary detailed sectional view of a mold used in practicing my process;

Fig. 4 is a section thereof taken substantially along the plane 4- 1 of Fig. 3;

Fig. 5 is a fragmentary detailed sectional view of another form of mold used in practicing my invention;

Fig. 6 is a section thereof taken substantially along the plane 6-6 of Fig. 5; and

Fig. 7 is a front elevation of a cast rotary saw 4 blade formed in the mold shown in Figs. 5 and 6.

In practicing my process, a molten tungsten carbide mass is first produced as by the aid of the invention disclosed by the prior Patents 1,719,558, issued July 2, 1929, and 1,721,966, issued July 23, 1929, to Oscar L. Mills. This mass is heated to a temperature above its melting point, and has, by weight, not less than 2 percent of carbon, nor more than 6 percent thereof in the preferred form. It can be alloyed with other metals, but preferably there should not be more than 2 percent by weight of such materials or other impurities. Among such alloying metals may be mentioned the iron group, chromium, molybdenum, tantalum, boron, silicon, thorium and titanium.

When the mixture is thoroughly and completeiy molten, as in a carbon or graphite crucibie capable of accommodating at least several pounds of the material, it is poured into a mold of the desired configuratioru'and subjected to pressure for the purpose ofsecuring a sharp defined product with a fine grain structure. The material is ,heated to a very high temperature; somewhere in the neighborhood of 5000 to 606-1) degrees Fahrenheit, in order to put it in the plastic or fluid state.

I prefer to cast the molten material in a mold that is capable of gradually and uniformly absorbing and transferring the heat from the product. Combination molds having a refractory mold proper made from graphite and an outer surrounding copper or silver jacket or mold are admirably suited for this purpose. Graphite will not materially react with the molten mass and due to its low heat conductivity gradually absorbs and transfers heat away from the product and thus aids in producing the desired casting without internal strains. The thickness of the graphite mold determined in accordance with the mass of the casting. In general, the larger the casting, the thicker this mold should be.

While the material is still molten, it is, subjected to pressure, as hereinabove set forth. A convenient way of accomplishing this is by the aid of centrifugal force. Thus the mold structure can be so arranged that it can be rotated to throw or urge the molten mass against it and in the graphite mold proper to cast the desired sharply defined prod ct.

I have indicated in the present instance'a combination mold structure that is capable of casting a product such as a hollow cylinder (Figs. 1-4) however, as will be hereinafter set forth, other sharply defined products can be cast.

The combination mold structure II! as shown most clearly in Figs. 1-4, comprises an outer shell or mold formed of copper, silver or the like, and

an inner graphite mold proper I l The outer mold l consists of a pair of hollowed out members l2 and is which when superimposed in abutting relationship, define a space in which the mold proper ll resides. There is a mold at each end of the member ID. The mold proper is confined in this space as by a pair of end members l4 formed of graphite, one at each end of member ID. Each of these end members may be provided with inwardly extending corrugations or ribs l5 which cooperate with one end of the mold proper to define air spaces !6' for a purpose and in a manner to be described. A pair of rigid L-shaped metailic end members or brackets l6 and I1 ahut agaimt the graphite end members is and overlie the ends of the members l2 and I3. Therigid end members l6 and I1 are rigidly secured to the outer mold ID as by bolts I 8 and I9 extemhng therethrough and into the channel member l3 in order to prevent the graphite end members l4 from becoming displaced or discharged during rotation. of the mold. This outer mold, as thus far described, is rigidly secured to a heavy metallic support or base 20 as by beits 2| and 22.

The top member E2 of the outer mold can be made relatively immovable with respect to the lower member l3 as by a pair of hooks 23. The hooks 23 cooperate with lugs 24 formed on the sides of the top member l2, and the legs thereof extend downwardly through openings 25 in the supporting member 20. A pair of interconnecting levers 25 are pivotally secured at one end to the ends of the legs of the hooks 23 as at 21, and are also pivot-ally secured at an intermediate point to-a pair of depending lugs 28 formed integral with the base 20. It is apparent that by a single downward movement of the levers 26, the hooks 23 will be lifted upwardly out of engagement with the lugs 24 and permit the reiative movement and separation of the top member I 2.

The upper member l2 can have a large central aperture 29 to permit the pouring of the molten material into the closed outer mold, which is rotated about a vertical, central axis, in order to throw the material under pressure into the mold proper II. The pressure thus attained may be of the order of 50 or 200 pounds per square inch, although higher or. lower values could be used. The lower member 13 can have a large saucerlike depression 30 in the top face thereof immediately below the aperture 20 in order to permit the moiten material poured in to accumulate therein.

The mold proper I l is adapted to be positioned in the outer mold ID in the space defined by members I2 and I3, one at each end thereof, although it is readily apparent that more than one can be so positioned by simply changing. the inner contour of the outer mold. The mold proper is formed completely of graphite and is shown in this instance as comprising a hollow tubular shell 3| having upstanding end portions or flanges 32 and 33 which abut against the inner periphery of the members l2 and I3. The shell 3| is made of the right thickness to assure a gradual but not too slow cooling of the molten material. In order to prevent the sagging or breaking of this shell, reinforcing wire strands 34 are wound therearound, and a graphite ring 35 is inserted between terial is to be cast. The end member 36 as well as the flange 32 abut against the tips of the ribs l5 and form with the members l4 the air spaces l6". These spaces serve as heat insulation spaces to prevent the quick transmission of heat from the mold proper to the copper portions l2, i

The forward end member 31 is provided with gates or ports 39 through which'the molten material is forced into the space defined by the mold proper upon rotation. Both of the end members may be provided if desired with central recesses 40 and 4| which provide a space for the formation of bosses on the ends of the cylinder to be cast.

It is apparent that the mold proper II is inserted in the outer mold prior to the pouring in of the molten material. This can be accomplished by removing member I! in a manner already outlined.

To provide the above mentioned rotation, I show in this instance a shaft 42 joined to the bottom of the base 20, that can be rotated by any source of motion. For example, in Fig. 1 I show shaft 42 supported in'a bracket structure 43 on table 44, and an electric motor 45 conveniently supported under the table, which drives the shaft.

A product, such as a cylinder, formed in the manner above described, is permitted to remain the mcid proper for a short interval or time to permit the gradual and uniform cooling thereessary delay incident to the opening of the mold. As hereinabove set forth, the arrangement of a combination mold in the manner and of materials described, assures the gradual, but not too slow, removal of heat from the product. When the product has assumed a self-sustaining form, it is placed in a space where it is still further gradually cooled. This can be accomplished by removing member l2 in the manner described.

A space for gradually cooling the product to room temperature can be formed by a box 46 that contains some powdered material that retains heat long enough to insure slow cooling. For example, a massof silica flour 4'! can be used in box 46. If desired, the sides and bottom of the container can be provided with a layer of heat insulating material. This slow cooling effectively prevents internal strains.

Although I have described in detail the formation of a cast tungsten carbide cylinder, my invention is equally applicable to the formation of any desired cast sharply defined body. Thus in Figs. -7 a combination mold is. shown for the formation of a cast rotary saw blade 48. The mold utilized in making this article is essentially the same both in principle and construction as the mold shown in Figs. 1-4; it differs therefrom merely in the specific construction of the mold proper, for making possible the casting of very thin articles.

The outer mold in this form of the invention, comprises as before, a top and bottom member l2 and I3, end members l6, and base 20. A graphite lining serves as a support and an insulation for the mold proper 52.

The graphite lining and support comprises a relatively thick walled hollow tubular member 49 coinciding with the contour of the space defined by members 12 and I3; and an end member 50 closing one end of the tube 49 and positioned adjacent the end metallic members It. Diametrical- 1y opposed slots or grooves 5| are formed in the inner periphery of the tube 49 for the reception of the graphite mold 52.

The mold proper 52 comprises two graphite disks 53 and 54 having a diameter substantially equal to the distance across slots 5|. A graphite ring 55 of the same diameter as the disks is sandwiched in between the disks, and is provided with inverse saw teeth 56 on. its inner periphery. A core 51 is positioned in a central recess in the disk 53 to provide an opening 59 on the saw blade 48. The disk 53 is formed with ports or gates 58 for the entry of the molten metal into the mold proper 52.

' The composite mold thus described is inserted in the slots 5| of the tube 49 and is positioned with its plane surfaces parallel to the longitudinal axis of the tube 49 and the outer mold. In actual practice, the mold proper is first positioned as described, in the tube 49, which is then placed in the outer mold by removing member I 2 in a manner already described. The mode of casting is similar to that described in conjunction with the showings in Figs. 1-4. When casting, a large mass of metal is cast around mold 52, in the space between the mold and the cylinder 49. This overlying heavy mass of metal keeps the heat in the mold which would otherwise cool too rapidly. Of course, with larger castings this expedient is unnecessary.

I claim:

1. The process of manufacturing thin castings made from material diflicult to fuse, which comprises pouring the fluid material from which the casting is to be made, into a mold and also around the outside of the mold.

2. The process of manufacturing thin castings made from material difficult to fuse, which comprises pouring the fluid material from which the casting is to be made, into a graphite mold, and also around the outside of the mold, and maintaining slow heat loss from said poured material.

3. The process of manufacturing castings from material having a very high melting point, such as alloys of tungsten carbide, which comprises placing a graphite mold in a massive support so as to hem good heat transferring relation to said support, rotating the support, and pouring the molten material into the support where it is urged by centrifugal pressure into the mold.

4. The process of manufacturing castings from material having a very high melting point, such as alloys of tungsten carbide, which comprises subjecting the mold to centrifugal force, and pouring the molten material from which the casting is to be made, in and around the mold.

ORRIN F. MARVIN. 

